Assume TS when the HLS segment URI has no path

Issue:#4033

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Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=190603518

library/hls/src/main/java/com/google/android/exoplayer2/source/hls/DefaultHlsExtractorFactory.java

@@ -52,6 +52,9 @@ public final class DefaultHlsExtractorFactory implements HlsExtractorFactory {
       Format format, List<Format> muxedCaptionFormats, DrmInitData drmInitData,
       TimestampAdjuster timestampAdjuster) {
     String lastPathSegment = uri.getLastPathSegment();
+    if (lastPathSegment == null) {
+      lastPathSegment = "";
+    }
     boolean isPackedAudioExtractor = false;
     Extractor extractor;
     if (MimeTypes.TEXT_VTT.equals(format.sampleMimeType)